1. Field of the Invention
The present invention relates to a fast-curing photosensitive composition that remains sensitive up to the visible range and that is used in recording inks, materials encapsulated inside photocuring microcapsules for image recording, photosensitive coating compositions, and the like; and to a recording sheet obtained using microcapsules inside which the fast-curing photosensitive composition is encapsulated.
2. Related Art of the Invention
Many conventional photosensitive compositions for image recording and the like are irradiated with lasers or the like, and are cured with the light energy thus produced. Many of these compositions are comprised of photopolymerization initiators (such as aromatic carbonyl compounds) and radical-polymerizable unsaturated compounds containing ethylenic unsaturated groups.
Photosensitive recording sheets are also known. These sheets are obtained by coating supports such as paper and resin films with photosensitive compositions or photosensitive microcapsules obtained by encapsulating such photosensitive compositions inside light-transmitting microcapsules.
Such photosensitive recording sheets are irradiated with light in accordance with image information, latent images are formed by allowing solely the regions irradiated with light to undergo curing, the recording sheet containing the latent images thus formed is then pressed or otherwise mechanically worked, and the uncured microcapsules are broken up, causing the dye precursor to flow out, react with the developer, and render the images visible, completing the recording.
The range of application of conventional photosensitive compositions is, however, very limited because these photosensitive compositions have a much lower photopolymerization initiation capacity with respect to light sources in the visible range (above 400 nm) than in the ultraviolet range (400 nm and less).
A photosensitive composition with higher sensitivity in the visible range is needed for achieving faster scanning exposure with low-energy light.
Several proposals have been made concerning photosensitive compositions that are sensitive to visible light. Examples of such proposals include complex initiator systems containing dyes and aliphatic amines (Japanese Patent Publication No.44-20189); systems containing hexaarylbiimidazoles, radical-producing agents, and dyes (Japanese Patent Publication No.45-37377); systems containing hexaarylbiimidazoles and p-dialkylaminobenzylidene ketones (Japanese Patent Application Laid-open No.47-2528); systems containing cyclic cis-.alpha.-dicarbonyl compounds and dyes (Japanese Patent Application Laid-open No.48-84183); systems containing carbonyl compounds and tertiary amines (Japanese Patent Application Laid-open No.52-134692); systems containing substituted triazine and merocyanine pigments (Japanese Patent Application Laid-open No.54-151024); systems containing biimidazoles and indanones (Japanese Patent Application Laid-open No.54-155292); systems containing hexaarylbiimidazoles and p-dialkylaminostylbene derivatives (Japanese Patent Application Laid-open No.57-21401); systems containing hexaarylbiimidazoles and p-dialkylaminocinnamylidene derivatives (Japanese Patent Application Laid-open No.58-19315); systems containing triazine derivatives and cyanine dyes (Japanese Patent Application Laid-open No.58-29803); systems containing triazine derivatives and thiapyrillium salts (Japanese Patent Application Laid-open No.58-40302); systems containing hexaarylbiimidazoles and n-dialkylstilbene derivatives or of p-dialkylaminophenyl butadienyl derivatives and thiol compounds (Japanese Patent Application Laid-open No.59-56403); systems containing ketone-substituted derivatives and organic peroxides (Japanese Patent Application Laid-open No.60-32801); systems containing .alpha.-diketones and mercaptocarboxylic acids (Japanese Patent Application Laid-open No.61-258802); and systems containing .alpha.-diketones and polysulfides (Japanese Patent Application Laid-open No.61-258803).
Photosensitive compositions containing these systems can indeed be polymerized when exposed to visible light, but they do not necessarily yield adequate cured products. A need therefore exists for photosensitive compositions highly sensitive to visible light, as is a need for photopolymerization initiators highly sensitive to visible light.